Concentrations of major ions and the 13C composition of dissolved inorganic carbon in groundwater and
submarine groundwater discharges (SGD) in the area between Siracusa and Ragusa provinces, southeastern
Sicily, representing coastal carbonate aquifers, are presented and discussed. Most of analyzed groundwater
belong to Ca-bicarbonate type, in agreement with the geological nature of carbonate host rocks. Carbonate
groundwater acquire, beside the dissolution of carbonate minerals, dissolved carbon (and the relative
isotopic composition) from the atmosphere and from soil biological activity. In fact, 13C values and TDIC
contents show that both these sources contribute to carbon dissolved species in the studied waters.
Finally, mixing with seawater resulted the second main factor of groundwater mineralization.